Multi-arm transducer bridge



July 12, 1966 K. s. LION 3,260,934

MULTI-ARM TRANSDUCER BRIDGE Filed Dec. 10, 1962 c ,,,4 cf) I 0-l :I

W/-+ R R INVENTOR KURT S LION BY W ATTORNEYS United States Patent Office 3,260,934 Patented July 12, 1966 3,260,934 MULTI-ARM TRANSDUCER BRIDGE Kurt S. Lion, 9 Herbert Road, Belmont, Mass.

Filed Dec. 10, 1962, Ser. No. 243,233 8 Claims. (Cl. 324-57) The present invention relates to multi-arm transducer bridge circuits, and, more specifically, to improved circuits of the type disclosed in the applicants earlier United States Letters Patent No. 3,012,192, issued December 5, 1961, embodying an alternating, varying or pulsating driving-voltage source, hereinafter generically referred to as a source of alternating-current voltage, and a D.-C.- level indicating or responding output circuit, hereinafter termed a direct-current voltage output circuit.

While eminently satisfactory bridge circuits are disclosed in thefsaid Letters Patent, particularly suitable for transducinginto voltages variable capacitive and inductive impedance changes, there are occasions where it is important that the variable impedance element be constituted of or comprise a variable resistance, such as in the case of resistance strain gauges and the like. It is to an improved circuit operating .with variable resistance elements that the present invention is accordingly primarily directed.

Another object of the invention is to provide a novel variable resistance bridge in which deleterious, spurious or stray signal components are obviated by the grounding of the source, the variable resistance elements and one terminal of the output circuit.

Still an additional object is to provide a new and improved bridge of more general utility, as well.

Other and further objects will be explained hereinafter and will be more fully set forth in the appended claims.

The invention will now be described in connection with the accompanying drawing, the single figure of which is a schematic circuit diagram of a preferred embodiment.

A source S of alternating-current voltage of any desired low or high frequency type, as described in the said Letters Patent, is connected between input terminals 1-1, the former of which is grounded, as at G. The term ground as herein employed is intended to embrace not only actual earthing, but chassis or other reference potential, also.

The parallel-connected arms of a first pair of similar bridge arms are connected between the input terminals 1-1,-the arm-s comprising respective rectifiers D and D in series with respective variable resistance elements R and R The variation of one or both of the resistance elements R and R is to be transduced into direct-current output voltages in an output circuit 4, connected between output terminals 1" and 1", the former of which is common with the grounded input terminal .1. Connected in the output circuit 4 is any desired direct-current voltage load or indicator, such as a meter M. The rectifiers are shown connected with opposite electrodes (anode, cathode) connected to the input terminal 1.

The parallel-connected arms of a second pair of similar bridge arms are connected between the output terminals 1"-1"', these arms comprising respective energy-storage fixed-value capacitors C and C in series with respective fixed-value resistors R and R Conductors 2 and 2' connect respective capacitors C and C in parallel with the respective resistance elements R and R The time-constant values of the parallel-connected capacitor-variable resistance networks C -R and C R are adjusted with respect to the period of the source frequency to enable substantial storage and discharge of rectified voltage in the capacitors C and C at the frequency of the source S; and the value of resistances R 'and R is made much larger than that of the elements R and of the impedance at the said frequency of the networks C -R and C2-R2, in order to insure this storage and discharge action, with sensitive variation in directcurrent output voltage at M resulting for slight variations of either or both of the resistance elements R and R I As an illustration, the resistance elements R and R may be resistance strain gauges or the like each of which is exposed to common and thus compensatory temperature conditions and variations, and one of which R as schematically illustrated by the dotted gang indication G is to be subjected to, or varied with, forces from some source or apparatus. Clearly, other types of signal control of the elements R and/or R may also be effected.

An example of a successful circuit of this character involves silicon diode rectifiers D D of the Hughes Type 561, a 10-kilocycle source S of 25-volt R.M.S. output, substantially equal fixed resistors R and R of about 500K ohms, substantially equal fixed capacitors C and C of about 0.01 ,ufarad, and a vacuum-tube voltmeter M for measuring direct-current output voltages of up to 1 /2 volts for variations in R and/or R up to 12K ohms. If both R and R are to be varied, they should preferably be varied in opposite directions as indicated by the oppositely headed arrows therethrough, thus to produce a dilferential efiect. It should be noted, moreover, that since R and R are grounded, no spurious or stray signals are introduced; whereas if R and/ or R were varied, variations in capacitance between them and ground would decidedly introduce stray undesired signals.

Further modifications will occur to those skilled in the art and all such are considered to fall within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. A transducer multi-arm bridge having, in combination, a pair of input and a pair of output terminals one of each of which is common and is grounded, means for applying alternating-current voltage of predetermined frequency between the pair of input terminals, a directcurrent voltage output circuit connected between the pair of output terminals, a first pair of similar arms connected in parallel with one another between the said one common terminal and the other of the said pair of input terminals and each comprising a rectifier and a series-connected resistance element variation of which may be transduced into an output signal in the output circuit, a second pair of similar arms connected in parallel with one another between the said one common terminal and the other of the said pair of output terminals and each comprising an energy-storage element and series-connected resistance of value greater than the resistance of the said resistance elements, each of the energy-storage elements being connected in parallel with one of the said resistance elements and the time-constant of each energy-storage element and its parallel-connected resistance element being adjusted to enable substantial storage and discharge of rectified voltage at the frequency of the alternating-current voltage.

2. A transducer bridge as claimed in claim 1 and in which each resistance element comprises a resistance strain gauge.

3. A transducer bridge as claimed in claim 2 and in which each of the resistance-element strain gauges is exposed to common temperature variations and one of the same is subjected to strain variations that are to be transduced into output-circuit signals.

4. A transducer bridge as claimed in claim 1 and in which the rectifiers have opposite electrodes thereof connected to the said other input terminal.

5. A transducer bridge as claimed in claim 1 and in which the resistance elements of each oi the first pair of arms have a common terminal that is connected to the common grounded input-output terminal.

6. A transducer bridge as claimed in claim 1 and in which one only of the said resistance elements is varied.

7. A transducer bridge as claimed in claim 1 and in which the said resistance of each of the second pair of arms is of value greater than the impedance of each of the said parallel-connected energy-storage and resistance elements at the said predetermined frequency.

8. A transducer as claimed in claim 1 and in which the energy-storage elements comprise capacitors fixed at substantially equal values and the said resistances of the second pairs of arms are fixed at substantially equal values.

References Cited by the Examiner UNITED STATES PATENTS 3,012,192 12/1961 Lion 32457 OTHER REFERENCES Nielsen, D.M.: Strain Gages, in Electronics, December 43, pages 106-111 and 192-194.

WALTER L. CARLSON, Primary Examiner.

G. L. LETI', Assistant Examiner. 

1. A TRANSDUCER MULTI-ARM BRIDGE HAVING, IN COMBINATION, A PAIR OF INPUT AND A PAIR OF OUTPUT TERMINALS ONE OF EACH OF WHICH IS COMMON AND IS GROUNDED, MEANS FOR APPLYING ALTERNATING-CURRENT VOLTAGE OF PREDETERMINED FREQUENCY BETWEEN THE PAIR OF INPUT TERMINALS, A DRIECTCURRENT VOLTAGE OUTPUT CICUIT CONNECTED BETWEEN THE PAIR OF OUTPUT TERMINALS, A FIRST PAIR OF SIMILAR ARMS CONNECTED IN PARALLEL WITH ONE ONOTHER BETWEEN THE SAID ONE COMMON TERMINAL AND THE OTHER OF THE SAID PAIR OF INPUT TERMINALS AND EACH COMPRISING A RECTIFIER AND A SERIES-CONNECTED RESISTANCE ELEMENT VARIATION OF WHICH MAY BE TRANSDUCED INTO AN OUTPUT SIGNAL IN THE OUTPUT CIRCUIT, A SECOND PAIR OF SIMILAR ARMS CONNECTED IN PARALLEL WITH ONE ANOTHER BETWEEN THE SAID ONE COMMON TERMINAL AND THE OTHER OF THE SAID PAIR OF OUTPUT TERMINALS AND EACH COMPRISING AN ENERGY-STORAGE ELEMENT AND SERIES-CONNECTED RESISTANCE OF VALUE GREATER THAN THE RESISTANCE OF THE SAID RESISTANCE ELEMENTS, EACH OF THE ENERGY-STORAGE ELEMENTS BEING CONNECTED IN PARALLEL WITH ONE OF THE SAID RESISTANCE ELEMENTS AND THE TIME-CONSTANT OF EACH ENERGY-STORAGE ELEMENT AND ITS PARALLEL-CONNECTED RESISTANCE ELEMENT BEING ADJUSTED TO ENABLE SUBSTANTIAL STORAGE AND DISCHARGE OF RECTIFIED VOLTAGE AT THE FREQUENCY OF THE ALTERNATING-CURRENT VOLTAGE. 